Effect of multiply excited states to the EUV emission from yttrium-like tin

The spectral emission rate of yttrium-like tin (Sn11+) is investigated as the typical ion, which has a strong emission of extreme ultra-violet (EUV) light near the wavelength of 13.5 nm. The energy level structure of the tin ion is investigated using the non-relativesitic configuration average model to calculate the population in the local thermodynamic equilibrium, and the spectral structure of the unresolved transition array that has EUV emission is investigated based on the calculated atomic data using the HULLAC code. It is shown that the broad main peak is accompanied by the tail structure for shorter and longer wavelengths, which arises from multiply and inner-shell excited levels. The emission channels that significantly contribute to the spectrum are determined from a convergence analysis. The excited states below the ionization limit with a large population are shown to have a significant contribution to the emission.